Author Response

We thank Dr Haley for his thoughtful commentary. We appreciate this opportunity to expand our position. We certainly agree with Dr Haley that further studies are needed to determine the effect of ambulation with assistive devices on academic performance not only for children with myelomeningocele, but for children with any physical disability. We also recognize the limitation of single-subject research when generalizing findings from one or a few subjects. In group designs, generalizability is accomplished through random selection of relatively large samples from homogeneous populations. Children receiving physical therapy services, however, are often from heterogeneous populations with low incidences of physical disability. Findley et al1 found only 77 adolescents between the ages of 10 and 16 years who had myelomeningocele in the entire state of Minnesota, when age and the presence of myelomeningocele were the only qualifying criteria.